The present invention relates to a test socket for use in testing the electrical characteristics of an electronic device or a semiconductor package, and more particularly, to the structure of a contact for use in establishing electrical connection when the contact is brought into contact with an external connection terminal of an electronic device or a semiconductor package.
As shown in FIG. 19, a known test socket for use in testing an electronic device, such as an IC or a bare chip, or a semiconductor package, comprises a contact 1 which is formed by means of punching a member having the property of a spring into a predetermined shape, and a housing 11 which fixedly retains the contact 1 and is formed from an insulating material. In order to test a semiconductor package 14, the semiconductor package 14 is placed on a seat 13, and the tip end of the contact 1 is brought into contact with external connection terminals 14a extending from the semiconductor package 14. A press jig 12 is pressed against the external connection terminals 14a, to thereby establish electrical connection between the external connection terminals 14a and the contact 1. A predetermined test signal is transmitted to and received from electrical circuits provided within the semiconductor package 14, by way of the contact 1 and the external connection terminals 14a. 
FIG. 20 is a plan view showing the contact 1 provided in the known test socket shown in FIG. 19. In the drawing, reference numeral 1 designates a contact; 2 designates a resilient section; 3 designates a tip end which is to be brought into contact with external connection terminals of an electronic device or a semiconductor package; 4 designates a base; and 5 designates a terminal. The terminal 5 to be connected to a test circuit board protrudes downwardly from the base 4, which is provided for positioning the test socket and extends horizontally. The resilient section 2 protrudes from the base 4 upwardly while being bent horizontally. The tip end 3 is provided at the free end of the resilient section 2 and is imparted with elasticity with respect to the vertical direction. The press jig 12 is pressed against the external connection terminals 14a while the external connection terminals 14a of an electronic device or the semiconductor package 14 are placed on the tip end 3. As indicated by a dotted line shown in FIG. 20, the tip end 3 is displaced downwardly while involving horizontal movement and deflecting the U-shaped resilient section 2. By means of the restoration force of the deflected resilient section 2, the tip end 3 is brought into pressing contact with the external connection terminals 14a. 
FIG. 21 is a plan view showing the shape of a contact described in the Unexamined Japanese Patent Application Publication No. Hei 5-104856. In the drawing, reference numeral 1 designates a contact; 2a and 2b designate resilient sections; 3 designates a tip end; 4 designates a base; 5 designates a terminal; and 6 designates a support section. In the contact 1, the terminal 5 protrudes downwardly from the horizontally-extending base 1, and the support section 6 protrudes upward from the base 4. The base end of a first resilient section 2a and the base end of a second resilient section 2b are connected to the support section 6 such that the first and second resilient sections 2a and 2b extend horizontally while being spaced a certain distance apart from each other in the vertical direction. The tip end 3 to be brought into contact with the external connection terminals 14a of an electronic device or the semiconductor package 14 is connected to the free end of the first resilient section 2a and the free end of the second resilient section 2b. Vertical elasticity is imparted to the tip end 3. The contact 1 can retard horizontal movement of the tip end 3, which would otherwise be involved at the time of downward movement of the tip end 3, by means of the first resilient section 2a and the second resilient section 2b. As a result, there can be prevented disengagement of the external connection terminals 14a of an electronic device or the semiconductor package 14 from the tip end 3, or deformation of the external connection terminals 14a, which would otherwise be caused when the semiconductor package 14 is displaced while the external connection terminals 14a are disengaged from the tip end 3.
FIG. 22 is a plan view showing the shape of a contact described in the Unexamined Japanese Patent Application Publication No. Hei 4-34380. In the drawing, reference numeral 1 designates a contact; 2a and 2b designate resilient sections; 3 designates a tip end; and 5 designates a terminal. The contact 1 is formed by means of vertically stacking two hair-pin-like resilient sections 2a and 2b so as to constitute an S-shaped geometry, and attaching the tip end 3 to an upper free end of the two resilient sections 2a and 2b. The terminal 5 is attached to a lower free end of the two resilient sections 2a and 2b. The two resilient sections 2a and 2b are bent in opposite directions, and hence the contact 1 having the resilient sections 2a and 2b has the function of retarding horizontal movement, which would otherwise be involved by vertical movement of the tip end 3.
The surfaces of the external connection terminals 14a of an electronic device or the semiconductor package 14 are usually plated, and an oxide film is formed on the surface of the external connection terminals 14a. Hence, the external connection terminals 14a have high electrical resistance. There is a necessity for establishing good electrical contact between the external connection terminals 14a and the tip end 3 of the contact 1 by means of removing the oxide film and increasing the area of contact between the external connection terminals 14a and the tip end 3. FIG. 23 is a perspective view showing the shape of a contact 1 which is to realize good electrical contact and is described in the Unexamined Japanese Patent Application Publication No. Sho 58-199545. In the drawing, reference numeral 1 designates a contact; 2 designates a resilient section; 3 designates a tip end; 3a designates a protuberance; and 5 designates a terminal. In the contact 1 having such a structure, a plurality of protuberances 3a are formed in the tip end 3 with which the external connection terminals 14a are to be brought into contact. Even in a case where an oxide film is formed on the surface of the external connection terminals 14a, the contact 1 has the function of breaking the oxide film, to thereby ensure electrical contact with the external connection terminals 14a. 
In the known contact shown in FIG. 20, external connection terminals are moved horizontally by several hundreds of micrometers when contact pressure is applied to the external connection terminals, as a result of which the external connection terminals are disengaged from the tip end. Use of either one of the contacts shown in FIGS. 21 and 22 prevents disengagement of the external connection terminals from the contact, which would otherwise be caused by horizontal movement of the external connection terminals. Such a known contact involves external connection terminals being moved about 50 μm horizontally and fails to eliminate relative sliding movement, which would arise between the tip end 3 of the contact and the external connection terminals 14a. The external connection terminal 14a is formed from a 42-alloy, and solder plating having a thickness of about 10 μm is formed on the surface of the external connection terminal 14a. Since the surface of the solder plating is naturally oxidized, the surface of the external connection terminal 14a is coated with an oxide. In a case where relative sliding movement arises between the external connection terminals 14a and the tip end 3, the tip end 3 scrapes a solder or solder oxide which covers the external connection terminals 14a. The resultant agglomerate adheres to and are accumulated on the surface of the tip end 3. Particularly in a case where the accumulated agglomerate corresponds to insulating oxides, electrical connection is hindered. As a result, the semiconductor package may be erroneously determined to be defective even though the semiconductor package is non-defective. In contrast, in a case where the accumulated agglomerate is conductive oxides such as solder, high contact resistance arises between the external connection terminals and the tip end 3, and the semiconductor package may be erroneously determined to be defective. In either case, an electronic device or semiconductor package, which has been determined to be defective, is uneconomically discarded. In order to prevent occurrence of uneconomical discarding of a non-defective electronic device or semiconductor package, a test socket must be replaced with a new one after a short period of use. This accounts for the shortening of the life of a test socket for testing an electronic device or a semiconductor package.
In the case of use of a contact having protuberances provided on its tip end shown in FIG. 23, good electrical contact can be achieved during an early period. Bringing external connection terminals in contact with the tip end of the contact involves horizontal movement of the external connection terminals. Further, the surface of the external connection terminals is scraped by the sharp protuberances, which inevitably involves formation of a large amount of agglomerate. As in the case of the previously-described background art, the life of the test socket is shortened.
Either of the previously-described contacts involves horizontal movement of external connection terminals, which in turn results in formation and deposition of agglomerate. The resultant agglomerate is scraped from the external connection terminals as a result of repeated used of the contact. In a case where agglomerate is conductive and adheres to external connection terminals so as to extend across the contacts, electrical shortcircuit may arise. Further, the agglomerate that adheres to the external connection terminals causes soldering failures when a semiconductor package is mounted. In association with an increase in the size of an electronic device or semiconductor package and the number of terminals, a pitch between external connection terminals is made narrower, and hence agglomerate imposes a serious problem.
Besides, generally, an electric device or a semiconductor package 14 are protected by resin molding. After molding, unnecessary resin is cut off. During cutting off, resin trash sometimes attaches to external terminal 14a. The trash avoids electric connection between a contact terminal and the external terminal. Due to this, a good electric device or a good semiconductor packaging are deteriorated.